1. Field of Application
The present invention relates to a radome incorporating a partition wall for providing enhanced isolation between transmitted and received radar waves, and to a radar apparatus incorporating the radome.
2. Description of Related Art
Types of radar apparatus are known, in particular for installation in a vehicle for detecting target objects ahead of the vehicle, which transmit/receive radar waves in the millimeter-wavelength range. Such a radar apparatus typically employs a planar antenna structure, in which a transmission section is formed of a pattern of conductive material formed on a planar face of substrate and a receiving section is similarly formed of a pattern formed on a substrate. An example of this is illustrated in the cross-sectional view of FIG. 4A, in which the antenna has a transmitting antenna section 151 and a receiving antenna section 153 which are both formed on the same face of a antenna substrate 150, for compactness. That face is referred to in the following as the antenna formation face. However with such a configuration it is difficult to achieve a sufficient degree of isolation between transmitted and received waves. That is to say, it is difficult to sufficiently reduce the strength of transmitted radar waves from the transmitting antenna section 151 which are directly received by the receiving antenna section 153 (i.e., which “leak” to the receiving antenna section 153 from the transmitting antenna section 151), instead of being received only after reflection from a target object.
Such directly received radar waves are indicated by the arrow lines in FIG. 4A, and produce increased reception noise. This causes the noise floor of the received signal to be raised, thereby lowering the detection performance (e.g., reducing the maximum range at which target objects can be detected).
Furthermore as illustrated in the cross-sectional view of FIG. 4B, when a radome 130 is provided, formed of a material which is transparent to radar waves and which covers the transmitting antenna section 151 and receiving antenna section 153, some transmitted waves are reflected from the internal face of the front wall 130 towards the receiving antenna section 153. These reflected waves act to further reduce the isolation between transmitted and received waves.
For that reason it has been proposed (e.g., in Japanese patent application publication No. 10-126146) as illustrated in FIG. 5, to increase the isolation between transmitted and received waves by installing a partition wall 160, formed of a metal plate, or a plate of a material which absorbs radar waves. This is mounted on the antenna formation face of the antenna substrate 150, between the transmitting antenna section 151 and the receiving antenna section 153. However with such a method, it is necessary to provide and install a partition wall 160 which is formed of a different material from that of the antenna substrate 150. This raises the problem of increasing the number of component parts required for manufacturing the radar apparatus, and additional manufacturing operations for attaching the partition wall 160 to the antenna substrate 150. Thus there is the disadvantage that the overall manufacturing cost of the radar apparatus becomes increased, due to incorporating the partition wall.